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    <meta charset="utf-8">
    <title>菜鸟教程(runoob.com)</title>
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    <!-- 
        基本类型：number，string，Boolean，null，undefined，symbol
        引用类型：Object，array，function，还有两个特殊的：RegExp,Date
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    <p id = "div">我的第一个段落。</p>
    <script>
        var doc = document.getElementById("div");
        doc.innerHTML = typeof "john" + "<br>" + 
                        typeof 3.14 + "<br>" +
                        typeof false + "<br>" +
                        typeof [1,2,3,4] + "<br>" +
                        typeof {name:'john', age:34};
    </script>

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